This invention relates generally to the use of a liquid crystal material to selectively control light transmission through a transparent panel. Specifically, this invention relates to the use of a liquid crystal material to provide a window shade of selected transmittance, in combination with a dual pane heat insulating window panel (thermal-pane window).
Thermal-pane windows conventionally make use of spaced dual panes to provide a thermal barrier restricting heat conduction between the outside and the inside of a building and therefore tending to reduce heating and cooling costs. To further reduce cooling costs, window shades or blinds are used to block out intense, direct rays of sunlight, since conventional windows, insulating or otherwise, have little effect on radiative heat transfer. However, in using a conventional shade to eliminate sun glare, the view to the outside is blocked, which may be considered a visually unattractive result. The present invention overcomes this limitation without sacrificing energy efficiency by providing an electro-optical shade as an integral part of a thermal pane window. The room occupant may select the degree of light transmittance of the shade, thus eliminating glare and the adverse effect on cooling requirements from direct rays of the sun, while not blocking the view to the outside.
The present invention makes use of liquid crystal material to selectively control the intensity of light transmission through a window. Generally, use of liquid crystal materials to selectively control light transmission through a transparent panel is known. Representative patents disclosing the nature of liquid crystal materials and their use are U.S. Pat. No. 3,322,485 "Electro-optical Elements Utilizing an Organic Nematic Compound" issued Apr. 30, 1967, to R. Williams and U.S. Pat. No. 4,005,928 "Nematic Liquid Crystal Displays for Low Voltage Direct Current Operation" issued Feb. 1, 1977, to A. Kmetz.
The term "electro-optical liquid crystal cell" as used hereinafter is intended to mean a volume of liquid crystal material between two closely spaced electrodes, the liquid crystal material being electro-optically responsive to an electric field between the energized electrodes, such that light transmittance through the liquid crystal material is selectable depending upon the field strength. Further details are given below.